iv PREFACE. 



which rest upon them. Many of my views are diametrically 

 opposed to those usually received. In such cases the accepted 

 view has been given as well as my own. 



Every student will acknowledge that the morphology of 

 Arthropods has made immaterial advances during the past 

 fifty years when compared with that of Vertebrates ; yet an 

 immense number of new observations have been recorded. 

 This is sufficiently proved by the enormously increased litera- 

 ture upon the subject. 



I have availed myself largely of this accumulated literature, 

 but I have never allowed myself to be guided by mere text- 

 book statements, unless these on investigation have been found 

 consistent with my own observations. Many may possibly 

 depreciate my want of faith in statements which have been 

 repeated until they appear to be almost incontrovertible ; but 

 I am content to await the verdict of posterity on my con- 

 clusions. Some of my views will, of course, be replaced by 

 others, but I have the strongest belief that most of them will 

 withstand adverse criticism, and will ultimately be accepted. 

 If this is so, many of the old statements will disappear from 

 future text-books as completely as the Vertebrate morphology 

 of fifty years ago has vanished from those of to-day. 



